diff --git a/src/password_manager/vault.py b/src/password_manager/vault.py
index 36ca8a7..08561de 100644
--- a/src/password_manager/vault.py
+++ b/src/password_manager/vault.py
@@ -1,7 +1,8 @@
 """Vault utilities for reading and writing encrypted files."""
 
 from pathlib import Path
-from typing import Optional
+from typing import Optional, Union
+from os import PathLike
 
 from .encryption import EncryptionManager
 
@@ -12,9 +13,13 @@ class Vault:
     INDEX_FILENAME = "seedpass_passwords_db.json.enc"
     CONFIG_FILENAME = "seedpass_config.json.enc"
 
-    def __init__(self, encryption_manager: EncryptionManager, fingerprint_dir: Path):
+    def __init__(
+        self,
+        encryption_manager: EncryptionManager,
+        fingerprint_dir: Union[str, PathLike[str], Path],
+    ):
         self.encryption_manager = encryption_manager
-        self.fingerprint_dir = fingerprint_dir
+        self.fingerprint_dir = Path(fingerprint_dir)
         self.index_file = self.fingerprint_dir / self.INDEX_FILENAME
         self.config_file = self.fingerprint_dir / self.CONFIG_FILENAME
 
diff --git a/src/tests/test_concurrency_stress.py b/src/tests/test_concurrency_stress.py
new file mode 100644
index 0000000..e96012b
--- /dev/null
+++ b/src/tests/test_concurrency_stress.py
@@ -0,0 +1,72 @@
+import sys
+from pathlib import Path
+from multiprocessing import Process, Queue
+from cryptography.fernet import Fernet
+import pytest
+
+sys.path.append(str(Path(__file__).resolve().parents[1]))
+
+from password_manager.encryption import EncryptionManager
+from password_manager.vault import Vault
+from password_manager.backup import BackupManager
+
+
+def _writer(key: bytes, dir_path: Path, loops: int, out: Queue) -> None:
+    try:
+        enc = EncryptionManager(key, dir_path)
+        vault = Vault(enc, dir_path)
+        for _ in range(loops):
+            data = vault.load_index()
+            data["counter"] = data.get("counter", 0) + 1
+            vault.save_index(data)
+    except Exception as e:  # pragma: no cover - capture for assertion
+        out.put(repr(e))
+
+
+def _reader(key: bytes, dir_path: Path, loops: int, out: Queue) -> None:
+    try:
+        enc = EncryptionManager(key, dir_path)
+        vault = Vault(enc, dir_path)
+        for _ in range(loops):
+            vault.load_index()
+    except Exception as e:  # pragma: no cover - capture
+        out.put(repr(e))
+
+
+def _backup(dir_path: Path, loops: int, out: Queue) -> None:
+    try:
+        bm = BackupManager(dir_path)
+        for _ in range(loops):
+            bm.create_backup()
+    except Exception as e:  # pragma: no cover - capture
+        out.put(repr(e))
+
+
+@pytest.mark.parametrize("_", range(3))
+def test_concurrency_stress(tmp_path: Path, _):
+    key = Fernet.generate_key()
+    enc = EncryptionManager(key, tmp_path)
+    Vault(enc, tmp_path).save_index({"counter": 0})
+
+    q: Queue = Queue()
+    procs = [
+        Process(target=_writer, args=(key, tmp_path, 20, q)),
+        Process(target=_writer, args=(key, tmp_path, 20, q)),
+        Process(target=_reader, args=(key, tmp_path, 20, q)),
+        Process(target=_reader, args=(key, tmp_path, 20, q)),
+        Process(target=_backup, args=(tmp_path, 20, q)),
+    ]
+
+    for p in procs:
+        p.start()
+    for p in procs:
+        p.join()
+
+    errors = []
+    while not q.empty():
+        errors.append(q.get())
+
+    assert not errors
+
+    vault = Vault(EncryptionManager(key, tmp_path), tmp_path)
+    assert isinstance(vault.load_index(), dict)
diff --git a/src/utils/file_lock.py b/src/utils/file_lock.py
index 8df6031..e90f86b 100644
--- a/src/utils/file_lock.py
+++ b/src/utils/file_lock.py
@@ -1,14 +1,15 @@
 """File-based locking utilities using portalocker for cross-platform support."""
 
 from contextlib import contextmanager
-from typing import Generator, Optional
+from typing import Generator, Optional, Union
+from os import PathLike
 from pathlib import Path
 import portalocker
 
 
 @contextmanager
 def exclusive_lock(
-    path: Path, timeout: Optional[float] = None
+    path: Union[str, PathLike[str], Path], timeout: Optional[float] = None
 ) -> Generator[None, None, None]:
     """Context manager that locks *path* exclusively.
 
@@ -29,7 +30,7 @@ def exclusive_lock(
 
 @contextmanager
 def shared_lock(
-    path: Path, timeout: Optional[float] = None
+    path: Union[str, PathLike[str], Path], timeout: Optional[float] = None
 ) -> Generator[None, None, None]:
     """Context manager that locks *path* with a shared lock.